Plug valves have long been known in the prior art as an effective means of controlling the flow of fluid in pipelines. In some cases the closure member is cylindrical in form and mates with a similarly shaped seat within the body of the valve. In other cases the plug is of tapered form and fits within a similarly tapered bore within the body. Also in some cases, the plug is in metal-to-metal contact with the tapered bore while in other cases a film of lubricant/sealant (hereinafter "sealant") is interposed between the surface of the plug and the tapered bore to augment the sealing properties of the closure member of the plug and to minimize the amount of torque required to turn the valve between its open and closed position. In all cases, however, a valve stem which is connected to the plug extends through an opening in the housing to the exterior of the body so as to provide a means of rotating the plug between its open and closed position. This presents a possible leakage path from the interior of the body to the exterior.
Various means of sealing this leakage path have been proposed and utilized in the past. Typical of such seals are those shown in U.S. Pat. Nos. 1,932,322; 2,651,490, 2,699,916; 2,715,412; 2,718,665; 2,876,987; 2,945,668; and 4,159,818. In some cases such as in U.S. Pat. Nos. 1,932,322; 2,945,668; 2,876,987 and 2,651,490, the seal is provided between axially extending surfaces on the body of the valve and the plug. In others as shown in the U.S. Pat. Nos. 2,715,412 and 2,718,665 the seal is provided between radially extending surfaces at the top of the plug and on the body. In U.S. Pat. No. 2,718,665 a sealing ring of polytetrafluoroethelene is interposed between the top of a cylindrical plug and a radial surface on the body. During assembly pressure is applied axially to the plug to force the seal ring into a tapered groove in the top of the plug and to force it into close sealing contact with the groove and the body. In still other cases such as shown in U.S. Pat. Nos. 2,699,916 and 4,159,818, the seal is provided both on axially extending surfaces and on radially extending surfaces.
In all of these cases however, the sealing means employed or the method of providing the seal in the assembly is either relatively complicated and therefore expensive or is of doubtful effectiveness in providing an adequate seal. Moreover in lubricated tapered plug valves where a film of sealant is interposed between the plug and the tapered bore to enhance sealability and to reduce turning effort of the plug, it is desirable to control the clearance between the plug and body tapered bore which results as the plug moves axially out of the body tapered bore as a result of pressure on the sealant, to an optimum value. If the clearance is so great as to require a thick film of sealant, the sealant may be too easily forced out of the space between the plug and the body by line fluid pressure and into the fluid pipeline. At the same time, the method employed to control the clearance must not produce forces which would bias the plug axially inward toward the tapered bore creating interface pressure which could result in high frictional resistance between the plug and body causing the valve to be difficult to operate. Applicants have developed a means of providing an effective seal between the body and the stem and of providing during assembly a control of the clearance between the plug and the body tapered bore.